1. Field of the Invention
This invention concerns a spandex filament of the type which has improved tack characteristics and more particularly, such a spandex filament having certain metallic soaps dispersed within it.
2. Description of the Prior Art
Spandex filaments are known to exhibit considerable tackiness, as compared to conventional textile filaments. The spandex filaments tend to stick to various surfaces and to cohere to each other, especially when wound up on a bobbin or other package. This tackiness can cause excessive unwinding tension (referred to hereinafter as "take-off tension") as well as frequent, large transients in take-off tension. As the age of wound-up spandex filaments increases, these effects of tackiness usually worsen. Excessive take-off tensions and transients cause fabric defects and other manufacturing difficulties, particularly in circular knit hosiery fabrics.
In the art, various substances are suggested for lubricating the surfaces of spandex filaments as a means of reducing the tackiness of the filaments. For example, Yuk, U.S. Pat. No. 3,039,895, discloses that certain finely divided metallic soaps dispersed in textile oils, make very useful finishes for this purpose. The soaps suggested by Yuk include certain metal salts of certain acids. The metal component of the soap is selected from lithium, sodium, potassium, rubidium cesium, magnesium, calcium, strontium, barium, zinc, cadmium and aluminum and the acid component is selected from saturated or unsaturated fatty acids having 8 to 22 carbon atoms. Magnesium stearate is particularly preferred. Yuk suggests that the metallic soap should amount to 2 to 20% by weight of the finish and that the finish, when applied to the surface of the spandex filaments, should amount to at least 3.5%, preferably more than 5%, by weight of the filaments.
Chandler, U.S. Pat. No. 3,296,063, discloses another finish that is useful in reducing spandex filament tackiness. The finish has as essential ingredients a minor proportion of polyamylsiloxane and a major proportion of polydimethylsiloxane. A preferred finish contains 10% polyamylsiloxane and 90% polydimethylsiloxane. For lubricating spandex yarns, Chandler suggests that the finish usually should amount to at least 1% by weight of the yarn and preferably from about 2% to about 4%. The finish can be applied to the filaments by conventional techniques, such as dipping, padding, and spraying or by addition of the finish to the spinning solution for extrusion simultaneously with the fiber-forming materials. Chandler states that in some instances, metallic soaps such as those disclosed by Yuk (e.g., zinc stearate and magnesium stearate) may be used in the finish in small amounts (i.e., less than about 2% by weight of the finish). However, Chandler then points out that use of his mixtures of polysiloxanes completely eliminates the need for such dispersed solids in the finish.
Among the best lubricating finishes that have been applied to the surfaces of commercial spandex filaments is one that contains finely divided magnesium stearate in a mixture of 10% polyamylsiloxane and 90% polydimethylsiloxane, with the magnesium stearate amounting to between 4 and 10% by total weight of the finish. Such a finish can provide the spandex filaments with average take-off tensions of about 0.2 to 0.5 gram (measured as described hereinafter) but still cannot eliminate the numerous, large tension transients.
To further reduce the effects of the spandex filament tackiness, the general practice has been to store freshly spun, lubricated and wound-up filaments for three to four weeks and then to rewind them onto another package. This decreases the average take-off tension to about 0.1 gram and substantially diminishes the tension transients, usually to less than 0.4 gram. However, further aging of the rewound filaments (e.g., for two months or more) can necessitate another rewinding. Although such storage-and-rewinding operations reduce the take-off tension and transients to desirably low levels, such operations are costly and time consuming.
It is a purpose of this invention to provide as-spun spandex filaments which are relatively nontacky, which do not increase significantly in tackiness with age, which exhibit low average take-off tensions and only small tension transients, and which eliminate the previously needed storage-and-rewinding steps.